JPH0351795B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for forming a metal compound layer on the surface of an article to be treated, in particular, a method of forming a metal compound layer on the surface of an article to be treated, using a molten chloride bath to form a layer of metal compounds, such as metal carbides or metal borides, on the surface of the article to be treated. The present invention relates to a method for forming a metal compound layer comprising: (Prior Art) Conventionally, various metals or non-metallic elements have been attached to the surface of metal materials, especially iron-based materials, in the form of carbides or borides for the purpose of improving surface hardness or wear resistance. method is known. Generally, the plating method, electrolytic or electroless molten salt bath immersion method, cementation method, thermal spraying method, discharge hardening method, etc. For example, the electroless molten salt bath immersion method involves melting the target metal in a molten boric acid or molten borate bath, and immersing the article to be treated in this.
This is a method in which a carbide or boride layer of the above metal is attached to the surface of the material to be treated. Generally, metal carbides or borides are hard and have high wear resistance, and are therefore widely used today as wear-resistant parts such as molds, jigs, tools, machine tools, and sliding parts of automobiles. (Problems to be solved by the invention) As described above, there are many treatment methods in practical use today, but the molten salt immersion method is a simple treatment method, so it is difficult to put it into practical use. This is an attractive method. In addition, the electrolytic molten salt immersion method is a method in which electrolysis is performed using the material to be treated as a cathode during the above-mentioned immersion, and the precipitation of metal compounds is promoted, but the processing operation is quite complicated and can be said to be an expensive process. Therefore, the present inventors conducted studies focusing on surface treatment using a molten salt bath. However, the metal compound layer formed on the surface of the article to be treated is required to be extremely stable, which means that in a normal molten chloride bath, many metal compounds will not be liberated, that is, they will not react. , the formation of such metal compounds was generally considered difficult. Traditionally, boric acid or borate baths have been used for this purpose. Here, the present inventor investigated various combinations of the composition of the molten salt and the type of metal compound added thereto, selected some of the most possible combinations in terms of reaction energy, and conducted the actual treatment. As a result, even metal oxides, which were conventionally thought to be non-reactive, change to metal fluoride ions in the presence of fluorides, and in the presence of such compounds, for example, metal carbides (or borides)
It was discovered that the treated surface easily precipitates on the surface of the article to be treated, and that the treated surface thus obtained adheres closely to the substrate and has excellent hardness, abrasion resistance, and further corrosion resistance, and has hereby completed the present invention. did. Here, the feature of the present invention is a method of forming a surface film consisting of a target metal compound on the surface of an article to be treated using a molten salt bath, and in which a fluoride-containing molten chloride bath is used for the above-mentioned purpose. A dipping bath is prepared by adding an oxide of the metal to be treated and an elemental metal or an alloy containing the metal, and then the article to be treated is immersed in the dipping bath for an appropriate time. This method forms a metal compound layer on the treated surface. The technical feature of the present invention is that metal fluoride ions of the target metal are formed in the molten chloride bath, and these are deposited as various metal compounds on the surface of the article to be treated. Therefore, metal fluoride ions are generated. To the extent that it does, the present invention is not limited to the specific metal compounds derived therefrom or the specific properties thereof. The precipitation reaction of the metal compound described above is accelerated when the metal compound is a carbide and the article to be treated contains carbon, so preferably the article to be treated is an iron-based material containing 0.1% by weight or more of carbon or Cemented carbide and even carbon fiber materials. Also,
When the metal compound is a metal boride, the article to be treated may be made of a boron-containing material. When adding an oxide of a desired metal to the molten salt bath, the immersion bath is prepared by also adding a single metal or an alloy. The present invention takes advantage of the advantages of a chloride bath, the molten chloride bath being comprised of at least one alkali metal or alkaline earth metal chloride; and in one embodiment, The fluoride is an alkali metal or alkaline earth metal fluoride. (Function) The above-mentioned molten chloride bath generally has a basic composition of KCl-BaCl ₂ to which is added a fluoride, for example, NaF. In addition, typical examples of molten chloride baths include NaCL, LiCl, _CaCl2 , etc., and examples of fluorides include NaF, KF, LiF,
There are _CaF2 , _BaF2, etc. Preferably, a bath composition consisting of alkali metal chloride-alkaline earth metal chloride-alkali metal fluoride is preferred. The specific composition ratio at that time is already clear to those skilled in the art, but in general, KCl−BaCl ₂ −NaF
In the case of the system, KCl is 5 to 95 mol%, BaCl ₂ is 5 to 95 mol%
~95 mol% and NaF is 5-50 mol%. If the fluoride content exceeds 50 mole percent, not only will the bath temperature become too high, but corrosion problems will occur. The type of target metal is not particularly limited, but
Since one purpose of the treatment method according to the present invention is to improve the wear resistance of the treated material, generally hard metals such as Cr, V, W, Mo, Ti, Zr.Hf, Nb,
These are metals of Group A, Group Va, and Group A of the periodic table, such as Ta. Such target metals are typically added to the molten chloride bath as oxides, in part as compounds, since they are readily available and generally easy to handle. , is advantageous. In addition, the other part is added as metal powder. This refers to the target metal or an alloy containing it,
For example, it may be added as a ferroalloy, etc.
This is also an advantage of the invention. In this way, when sodium metal fluoride is used as the fluoride, NaF in the molten salt reacts with the oxide, and metal fluoride potassium, soda, etc. are partially produced. and they are, respectively, for example, TiO ₂ →NaK ₂ TiF ₆ , Cr ₂ O ₃ →NaCrF ₃ ,
V ₂ O ₅ →Na ₃ VF ₆ , B ₂ O ₃ →KBF ₄ , WO ₃ →K ₃ WF ₆
It is. Then, they react on the surface of the treated metal to form TiC, Cr ₇ C ₃ , VC, and TiC, respectively.
BFe ₂ , Fe ₆ W ₆ C, etc. The immersion time and temperature vary depending on the type of target metal compound to be produced and the material of the article to be treated, but generally, treatment at 800 to 1000°C for one to several hours is sufficient. There is no limit to the amount of the target metal or alloy added, but it is generally 2 to 20%, preferably 5 to 15%. Similarly, the amount of metal oxide is 2 to 7
%, preferably 5-7%. Next, the present invention will be explained in more detail with reference to Examples. In this specification, "%" means "% by weight" unless otherwise specified. Example In this example, KCl, BaCl ₂ and
After adding 42.2, 20.2, and 37.6 mol% of NaF and heating and melting them, the temperature was lowered to 700℃,
Predetermined amounts of each metal oxide and alloy powder (ferroalloy) were added and sufficiently stirred to form an immersion bath. A test piece (JIS SKD11) having a steel composition shown in Table 1 was immersed in the immersion bath thus prepared for a predetermined time. The combinations of metal oxides and alloys used in this example were as shown in Table 2.

[Table] A series of experiments were conducted under various reaction conditions. The results are summarized in Tables 3 to 7. Table 3 summarizes data on the types of metal compounds produced and their coating thicknesses when dipping was carried out at various temperatures. The immersion time was 2 hours. For TiC, Cr ₇ C ₃ , VC, and BFe ₂ , the amount of coating tends to increase as the temperature rises;
In the case of Fe ₆ W ₆ C, when comparing 900°C and 1000°C, there is not much change in the amount of coating. Table 4 summarizes the data on the type of each metal compound and its coating thickness when the dipping time was varied. The immersion temperature was 1000°C. In the case of TiC, Cr ₇ C ₃ , VC, and Fe ₆ W _{6 ,} the amount of each coating gradually increases over time, but it is about 3
It is saturated around mg/ ^cm2 . On the other hand, in the case of BFe ₂ , the amount of coating increases considerably with the reaction time. Table 5 shows the amount of NaF at 0, 13.9, 37.6 and 44.5.
The coating amount of each metal compound when changed in mol% is summarized. The immersion temperature was 1000°C and the immersion time was 2 hours. In both cases, the amount of coverage increases as the amount of NaF increases. This is because the added metal oxide
This is thought to be because almost no dissolution occurs in the absence of NaF. However, the reason why Cr ₇ C ₃ is slightly coated is because Cr ₂ O ₃ has some solubility even in the absence of NaF. Table 6 shows the relationship between the amount of alloy added and the amount of coating.
The immersion conditions are the same as in Table 5. When 5, 10, and 15% by weight of alloy is added, almost no change in coating amount is observed for any of the metal compounds. However, when the alloy addition amount is 0%, the coating amount is also zero in both cases. In other words, the presence of an alloy (or an elemental metal) is essential for the reaction to proceed. Table 7 shows the change in coating amount when the amount of metal oxide was changed. The immersion conditions are the same as in Table 5. From the results shown in the table, as the amount of metal oxide added increases, the amount of coating tends to increase, albeit by a small amount. The reason why a coating was observed even when the amount of metal oxide was zero is thought to be because the oxide on the surface of the added alloy powder reacted with NaF, some metal fluoride ions were generated, and the reaction progressed. Thus, in the method according to the present invention,
The reaction will not proceed unless the alloy (or single metal) and metal fluoride ions are present at the same time. In other words, film formation will not occur unless the alloy (or single metal) coexists with the metal oxide and fluoride. Next, we used an immersion bath prepared by adding 15 g of KCl, 20 g of BaCl ₂ , 7.5 g of NaF, 1 g of metal oxide, and 5 g of alloy powder, and treated the film at 1000°C for 2 hours. We investigated its hardness and wear resistance. and corrosion resistance were tested. Table 8 shows the surface hardness of the above coatings as measured by a Micro-Vickers hardness meter. It can be seen that extremely high hardness can be obtained. Wear resistance tests were conducted using a reciprocating abrasion tester, and the results showed that almost no wear was observed on the specimens coated with TiC, Cr ₇ C ₃ , and VC. Regarding corrosion resistance, in H ₂ SO ₄ solution
TiC and VC, and in NaCl solution TiC,
Cr ₇ C ₃ and VC were particularly excellent. Although the present invention has been explained using carbides and borides as examples of metal compounds in the present invention, it is obvious to those skilled in the art that various other metal compounds are also conceivable, and the present invention also applies to them. shall be understood to apply. (Effects) As described above, according to the present invention, it is possible to obtain the same results as those obtained in a conventional borate bath or in combination with an electrolytic treatment by a simple immersion treatment using an easy-to-handle molten chloride bath. It is possible to obtain a surface film that is equivalent to or better than that obtained by
This will greatly contribute to the development of this industry. It is clear that the method of the present invention may be further combined with an electrolytic treatment method if necessary.

【table】

[Table] (Note) The inside of the cutlet is the film thickness.

[Table] (Note) The inside of the cutlet is the film thickness.

【table】

[Table] (Note) The inside of the cutlet is the film thickness.

[Table] (Note) The inside of the cutlet is the film thickness.

[Table] (Note) The inside of the cutlet is the film thickness.

【table】

Claims (1)

[Scope of Claims] 1. A method for forming a surface film consisting of a compound of a target metal on the surface of an article to be treated using a molten salt bath, the method comprising oxidizing the target metal in a fluoride-containing molten chloride bath. A dipping bath is prepared by adding a substance and a single metal or an alloy containing the metal, and then the surface of the article to be treated is immersed in the dipping bath for an appropriate time. A method of forming a metal compound layer. 2. The method according to claim 1, wherein the article to be treated is an article made of iron or an iron alloy containing 0.1% by weight or more of carbon. 3. The method according to claim 1 or 2, wherein the metal compound is a metal carbide. 4. The method according to claim 1 or 2, wherein the metal compound is a metal boride. 5. The method according to any one of claims 1 to 4, wherein the molten chloride bath comprises at least one of alkali metal and alkaline earth metal chlorides. 6 Claim 1, wherein the fluoride is an alkali metal or alkaline earth metal fluoride.
The method according to any one of Items 5 to 5.